This invention relates to communications networks and in particular to an arrangement and method for the routing of connectionless packet data in such networks.
Data networks based on packet protocols, such as Internet Protocol (IP), use addressing information in the packet header to determine the destination of individual packets. Since each packet is treated independently of any other packet, the networks are connectionless. Packets pass individually through the network between router nodes which determine to which router the packet should be sent next. The processing power required to interpret packet header information and determine the route to the next network node limits the capacity of the router.
A discussion of techniques for enabling a combination of IP and ATM technologies is given by Parulkar et al. in Computer Communications Review, Vol.25, No.4, Oct. 1, 1995, pages 49 to 58. A description of a connectionless data service for an ATM network is given by Box et al. in Networking: Foundation for the Future, San Francisco, Mar. 28-Apr. 1, 1993, Vol. 2, Mar. 28, 1993, IEEE, pages 722 to 731.
In many instances, a communication between two terminal nodes in a communications network involves transmitting many IP packets in sequence. This is commonly referred to as a xe2x80x98flowxe2x80x99. When a flow is identified by a router, a temporary link xe2x80x98connectionxe2x80x99 can be set up through the network to carry this flow. All packets with the same header information can then pass over this connection, avoiding the need to process the headers on an individual basis. This technique is known as IP switching.
With the introduction of broad band asynchronous transfer mode (ATM) networks, there is now a need for the transport of connectionless packet traffic over such networks, particularly with the introduction of IP voice services to provide Internet based telephony. However, Internet traffic is not readily adapted to real time communication over a broad band network owing to its connectionless format, its multiple routing hops and its typical packet length which does not match the standard ATM cell.
An object of the invention is to minimise or to overcome this disadvantage.
A further object of the invention is to provide an improved method of carrying IP packet traffic over a broad band network.
The present invention relates to the use of IP switching techniques to implement a scaleable distributed router using ATM Adaptation Layer 2 (AAL2) as the bearer for IP packets identified as part of a flow.
According to a first aspect of the invention, there is provided a broad band network adapted to carry packet traffic and comprising a plurality of interconnected nodes, which nodes comprise tandem switches (12) and edge switches (13), said edge switches each incorporating an IP network interface or adapter (21) and being interconnected by permanent virtual channels via said tandem switches, wherein each said edge switch incorporates a cut-through routing function (52) having a memory (53) associated therewith for storing packet header information and having means for comparing header information from incoming packets with said stored information whereby to identify those packets forming a flow, means for segmenting each said packet determined to be part of a flow into minicells for transmission in sequence order over a said permanent virtual circuit established across the network for that flow, and default router means (55) for processing the packet headers of each of those packets not identified as part of a flow so as identify for that packet a destination edge switch for that packet and for segmenting that packet for transport over a default permanent virtual channel to said destination edge switch.
According to another aspect of the invention there is provided a method of transporting flow based and non-flow based packet traffic in a broad band network comprising a plurality of interconnected nodes, which nodes comprise tandem switches (12) and edge switches (13), said edge switches each incorporating an IP network interface or adapter (21) and being interconnected by permanent virtual channels via said tandem switches, the method including storing at each said edge switch packet header information, comparing header information from incoming packets with said stored information whereby to identify those packets forming a flow, segmenting each said packet determined to be part of a flow into minicells for transmission in sequence order over a said permanent virtual circuit established across the network for that flow, processing the packet headers of each of those packets not identified as part of a flow so as identify for that packet a destination edge switch for that packet, and segmenting that packet for transport over a default permanent virtual channel to said destination edge switch.
A flow is defined as an established sequence of IP packets from a source to a destination comprising e.g. a file transfer or an Internet voice call. In our arrangement, the ATM network functions as a distributed router whereby the IP packets are routed to the correct destination. Where a packet is identified as forming part of a flow, the destination will have already been established so that the packet payload can be carried in minicells over the permanent virtual channel that has been provisioned for that flow.